The invention relates to a piezoelectric element which becomes deformed upon receipt of a supplied drive signal, to a piezoelectric actuator and a liquid ejecting head using such a piezoelectric element as a drive source.
A piezoelectric element is formed from piezoelectric ceramics or a piezoelectric macromolecular film utilizing a high molecular compound and becomes deformed upon receipt of supplied electric energy, wherein the piezoelectric ceramics is formed by compressing and sintering metal oxide powder, such as BaTiO3, PbZrO3, PbTiO3, which are piezoelectric materials and exhibit a piezoelectric effect. The piezoelectric element is in widespread use as a drive element for, e.g., a liquid ejecting head, a micropump, and a sounding body (a speaker or the like). Here, the liquid ejecting head ejects a droplet from a nozzle orifice. The liquid ejecting head is embodied as, e.g., a recording head to be used in an image recording apparatus such as a printer, a liquid-crystal ejecting head for use in manufacturing a liquid-crystal display, and a coloring material ejecting head to be used for manufacturing a color filter. Here, the micropump is an ultrasmall pump capable of ejecting a very small volume of liquid and used at the time of, e.g., delivery of a trace amount of chemical.
In the field of such a piezoelectric element, strong demand exists for high-frequency driving of the piezoelectric element, and an increase in the rigidity of the piezoelectric element is sought. In the case of the recording head, the piezoelectric element is driven at a high frequency of about 10 to 30 kHz. In order to improve the durability of the piezoelectric element under such a driving condition, the rigidity of the piezoelectric element must be increased. Here, the only requirement for increasing the rigidity of the piezoelectric element is to increase the thickness of the piezoelectric layer. In this case, in order to ensure achievement of sufficient rigidity, a drive voltage must be increased, which is not suitable for high-frequency driving.
A piezoelectric element of multilayer structure is proposed as a piezoelectric element which achieves required rigidity and can be driven at substantially the same drive voltage as that conventionally employed. For instance, Japanese Patent Publication No. 2-289352A discloses a piezoelectric element which is formed from a piezoelectric layer having a two-layer structure; that is, an upper layer piezoelectric substance and a lower layer piezoelectric substance. Drive electrodes (individual electrodes) are formed at a boundary between the upper layer piezoelectric substance and the lower layer piezoelectric substance. A common electrode is formed on an outer surface of the upper layer piezoelectric substance, and another common electrode is formed on an outer surface of the lower layer piezoelectric substance. Similarly, Japanese Patent Publication No. 10-34924A also discloses a piezoelectric element of multilayer structure.
In the case of the piezoelectric element of multilayer structure, the drive electrodes are provided at the boundary between the upper layer piezoelectric substance and the lower layer piezoelectric substance. Hence, an electric field, whose intensity is determined by an interval between the drive electrodes and the common electrodes (i.e., the thickness of each piezoelectric substance) and by a potential difference between the drive electrodes and the common electrodes, is imparted to the piezoelectric substances of respective layers. Therefore, in contrast with a piezoelectric element of monolayer structure formed by interposing a single-layer piezoelectric substance between the common electrode and the drive electrodes, the piezoelectric element can be deformed greatly at the same drive voltage as that conventionally required, even when the rigidity of the piezoelectric element is increased by increasing the overall thickness of the piezoelectric element to some extent.
However, mere use of the piezoelectric element of multilayer structure cannot achieve performances that meet recently-growing demand. Therefore, users are forced to use, as an actual product, a piezoelectric element of monolayer structure formed by interposing a single layer piezoelectric substance between a common electrode and drive electrodes.